What is the large white blob floating in the Gulf of Mexico near Florida?

Off the coast of Sanibel Island in Florida, a large, milky-white blob is floating in the ocean, worrying some spectators.

The main fear, according to the Fort Myers News-Press, was that the white water was trichodesmium, which can be a precursor to red tide. Red tide is a bloom of algae that kills certain marine life and can cause respiratory issues in humans, typically resulting in temporary beach closures.

Trichodesmium is known as sea sawdust because that’s what it tends to look like – sawdust sitting on the surface of the water. They can extend for miles and be visible from space, according to the Florida Fish and Wildlife Conservation Commission, and vary in color from brown, green, pink or red, but generally turn white after pigments decay.

So what does it have to do with red tide? Trichodesmium produces a certain type of nitrogen that the harmful algae uses, so it’s generally attracted to outbreaks of sea sawdust. Red tide needs the sea sawdust to bloom, though every time sea sawdust is found it doesn’t automatically mean red tide is unavoidable.

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Luckily for Sanibel Island, the white blob is not trichodesmium, according to the News-Press. It’s a byproduct of what Sanibel may be most famous for – its shells.

“It looks like calcium carbonate that's been stirred up,” Eric Milbrandt, director of the Sanibel-Captiva Conservation Foundation, told the News-Press. “The bottom is made mostly of shells, and the shells basically break up into dust.”

It’s far from the first time a blob in the Gulf or an ocean has stirred up curiosity.

Some divers off the coast of Turkey in 2015 found a transparent blob filled with countless dots just beneath the surface, and one expert told the Daily Mail that it was likely a squid egg mass. A similar mass was found in the Gulf of California in 2008.